Cast bodies, castable compositions, and methods for their production

ABSTRACT

A low-water-content castable composition produces cast products with an increased modulus of rupture, an increased cold crushing strength, and decreased porosity. The composition employs closed fractions of constituent particles with specified populations and specified gaps in the particle size distribution to produce these properties. The composition is suitable for refractory applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/675,272 filed Feb. 25, 2010, which is the U.S. national phase entryof international application PCT/US08/74578, filed Aug. 28, 2008, whichclaims priority from U.S. provisional application Ser. No. 60/969,024,filed Aug. 30, 2007; the entire teachings of these applications areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to castable compositions with reducedmatrix content, such as refractory compositions for lining the innerwalls of vessels and furnaces intended to receive liquid metal, glassand the like. It also relates to cast bodies produced from thesecompositions and methods.

BACKGROUND OF THE INVENTION

A number of processes for producing a lining on the inner walls of ametallurgical vessel are known. Thus, for example, there is known,according to the prior art, a process in which an aqueous and pastymixture capable of setting, containing inorganic particles, optionallyfibers, and an organic and/or inorganic binder, is applied by molding,tamping or projecting with a trowel, pneumatic tube or other projectingdevice to the inside of a metallurgical vessel such as a castingtundish. The mixture of particles sinters in contact with the liquidmetal, and this ensures the cohesion of the lining.

According to the prior art, there is also known a process according towhich at least two layers of different compositions are applied to theinside of the metallurgical vessel, each being applied by projecting anaqueous and pasty mixture capable of setting of the above-mentionedtype.

The fluidity of such aqueous and pasty mixtures, which expedites theirapplication, is proportional to the amount of wetting water present. Thewetting water employed for forming the aqueous mixture(s) must beremoved by drying, and this involves an immobilization time and anexpenditure of energy, neither of which can be ignored.

There is also known a process according to which a template is placedinside a metallurgical vessel, a material consisting of refractoryparticles and of a heat-curable binder is projected pneumaticallybetween the template and the inner walls of the vessel, and heating isthen applied while the template is left in place to cause the binder toset, and the template is finally removed. The cast material contains aninorganic compound containing water of crystallization. Water ofcrystallization is water in chemical combination with a crystal,necessary for the maintenance of crystalline properties but capable ofbeing removed by sufficient heat.

It is also known that refractory bodies can be made by casting ofrefractory concretes either by vibration casting of a wet concrete or byvibration-free casting of a concrete having a self-flowing consistency.In both approaches, all concrete materials need to be homogeneouslymixed and wetted. Customarily, matrix and coarse materials are batchedtogether. Then water is added to give fluidity and to initiate areaction that forms an end product of an ideal shape. To accomplishthis, a large portion of the material is fine-grained matrix material.This material has a high surface area, which lends itself to attack inadverse conditions, such as most refractory applications. Largerproportions of water improve the fluidity of the mixture, but promotethe formation of pores in the formed product. A high mixing watercontent in the castable means very long dry-out times and poormechanical strength. Smaller proportions of water inhibit poreformation, but yield product pieces that are prone to cracking,crumbling and spalling. In extreme cases, formulations using smallproportions of water are unable to form a coherent piece.

In order to increase thermal shock resistance, fibrous materials havebeen used in vibration-cast materials and in self-flowing materials. Theuse of fibrous materials increases the need for high levels of mixingwater and makes casting more difficult. Very coarse materials which arebeneficial for slag resistance due to their high density can only beused to a certain extent, because casting of concretes with a very highcontent of coarse materials is very difficult.

Infiltration processes are also used to produce objects containingcoarse particulates intermingled with finer particulates introduced inthe form of a slurry. For example, a mold may be filled with dry coarseparticulates which can have a size between about 1 and 60 mm to form aformed dry body. The formed dry body is then infiltrated with a slurryconsisting of a binder, water, and fine filler materials having aparticle size distribution of between 0.0001 to 3 mm. Infiltrationaccording to this method is a time-consuming process. The difficulty ofproduction of a thick piece by this method increases with the piece'sthickness, unless a larger aggregate is used.

The aim of the present invention is to overcome the disadvantages of theknown compositions and to produce a product in which the amount ofmixing water is minimized, the quantities of matrix material areminimized, the porosity of the formed dry body is minimized, the densityof the formed dry body is increased, and a product having enhancedmodulus of rupture and cold crushing strength values is produced.

BRIEF SUMMARY OF THE INVENTION

It has been found that certain compositional features, alone or incombination, yield castable materials that are able to be formulatedwith reduced amounts of water and exhibit increased density and reducedporosity when compared with the compositions of the prior art. Theseproperties can be imparted to a formed body in the absence of sintering.These features include:

1) The coarsest refractory grain fraction makes up 50% by weight orgreater of the dry composition; this fraction is separated from asmaller grain fraction by a gap having a ratio of smallest particlediameter to largest particle diameter such at least the square root of2, or at least 2. For example, the coarsest refractory grain fractionmay be composed of particles having diameters greater than 500, 800 or1000 micrometers, and may be a closed fraction having maximum particlesize, such as 1000, 2000 or 4000 micrometers.

2) The composition contains at least four grain fractions, of whichthree adjacent grain fractions, separated by gaps having a particlediameter ratio of at least the square root of two, or by gaps having aparticle diameter ratio of at least two, have remaining weightpercentages (percentage by weight of particle in the fraction withrespect to the weight of all particles in the fraction plus all smallerparticles) that are, with respect to the respective immediately largerparticle size fractions and in order of decreasing particle size,smaller, larger and smaller in value. This configuration (larger,smaller, larger, smaller fractions) is designated as an “alternatingremaining weight percentage” composition.

3) The composition contains at least four grain fractions, of whichthree adjacent grain fractions, separated by gaps having a particlediameter ratio of at least the square root of two, or by gaps having aparticle diameter ratio of at least two, have remaining weightpercentages (percentage by weight of particle in the fraction withrespect to the weight of all particles in the fraction plus all smallerparticles) that are, with respect to the respective immediately largerparticle size fractions and in order of decreasing particle size,larger, smaller and larger in value. This configuration (smaller,larger, smaller, larger fractions) is also designated as an “alternatingremaining weight percentage” composition.

4) The composition contains at least two, or at least three, grainfractions, separated by gaps having a particle diameter ratio of atleast the square root of two, or a particle diameter ratio of at leasttwo, entirely composed of particles with diameters less than 100micrometers.

5) The composition contains at least four grain fractions, separated bygaps having a particle ratio diameter of at least the square root oftwo, or a particle diameter ratio of at least two, in which theremaining weight percentages are at least 40%.

6) The composition contains at least five grain fractions separated bygaps having a particle ratio diameter of at least the square root oftwo, or a particle diameter ratio of at least two.

7) At least two of the gaps each contain less than 10 percent by mass,or less than 5 percent by mass, of the mass of the dry composition.

Compositions incorporating one or more of these characteristics havebeen produced in which, with weight percentages of water of 6.0 wt %,5.0 wt %, 4.0 wt %, 3.0 wt %, 2.5 wt % and 2.0 wt %, increased MOR(modulus of rupture), increased bulk density, decreased porosity andincreased CCS (cold crushing strength) values are obtained with respectto the prior art.

With compositions of the present invention, MOR values (measured inpounds per square inch) of 1000 or greater, 2000 or greater, 3000 orgreater, or 3500 or greater as measured after exposure to 230 degreesF., and 500 or greater, 1000 or greater, 2000 or greater, 3000 orgreater, or 3500 or greater as measured after exposure to 1500 degreesF., can be obtained.

With compositions of the present invention, bulk density values(measured in pounds per cubic foot) of 190 or greater, 195 or greater,or 200 or greater as measured at 230 degrees F., and 185 or greater, 190or greater, 195 or greater, or 200 or greater as measured after exposureto 1500 degrees F., can be obtained for formulations composed of 95 wt %alumina or greater.

With compositions of the present invention, porosities (measured asvolume percent) of 15 or less, 10 or less, 5 or less, 4 or less, or 3 orless as measured after exposure to 230 degrees F., and 18 or less, 15 orless, 10 or less, 5 or less, 4 or less, or 3 or less as measured afterexposure to 1500 degrees F., can be obtained.

With compositions of the present invention, CCS values (measured inpounds per square inch) of 3000 or greater, 5000 or greater, 8000 orgreater, 10,000 or greater, and 12,000 or greater as measured afterexposure to 230 degrees F., and 3000 or greater, 5000 or greater, 8000or greater, 10,000 or greater, and 12,000 or greater as measured afterexposure to 1500 degrees F., can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of weight percentage of composition fractions, plottedagainst particle size on a logarithmic scale, for compositions of theprior art and of the present invention;

FIG. 2 is a graph of weight percentage of composition fractions, plottedagainst particle size on a logarithmic scale, for a composition of thepresent invention;

FIG. 3 is a graph of volume percentage of composition fractions, plottedagainst particle size on a logarithmic scale, for a composition of thepresent invention;

FIG. 4 is a graph of volume percentage of composition fractions, plottedagainst particle size on a logarithmic scale, for a composition of thepresent invention;

FIG. 5 is a graph of weight percentage of composition fractions, plottedagainst particle size on a logarithmic scale, for a composition of theprior art;

FIG. 6 is a graph of weight percentage of composition fractions, plottedagainst particle size on a logarithmic scale, for a composition of theprior art; and

FIG. 7 is a graph of weight percentage of composition fractions, plottedagainst particle size on a logarithmic scale, for a composition of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

It has been found that the presence or combination of certaincompositional features produces a refractory product in which the amountof mixing water is minimized, the quantities of matrix material areminimized, the porosity of the formed dry body is minimized, the densityof the formed dry body is increased, and a product having enhancedmodulus of rupture and cold crushing strength values is produced. Theseproperties can be imparted to a formed body in the absence of sintering.

The coarse aggregates useful in practicing the present invention maycontain fused alumina or sintered alumina (tabular alumina), wholealumina balls, fused bauxite, fused and sintered mullite, fused andsintered magnesia, fused and sintered magnesia aluminum spinel, fusedand sintered zirconia, refractory bauxites, refractory kyanite,refractory andalusite, refractory sillimanite, silicon carbide orcombinations thereof.

The coarse aggregates useful in practicing the present invention canhave any shape. They can be spherical, blocky, rectangular or evenfibrous. In addition, they may be used alone or in combination.

The binder used in the matrix may contain calcium aluminate cement,alpha bond cement, Portland cement, mono-aluminum phosphate (MAP),clays, reactive alumina (such as AA 101), hydratable alumina, andcombinations thereof. In certain embodiments, the matrix materialaccording to the present invention does not contain cement.

Other raw materials used in the matrix may include reactive aluminas,calcined alumina, tabular alumina, fused alumina, mullite, carbon(graphite or carbon black), silicon carbide, zirconium dioxide,magnesium oxide, aluminum silicates (such as kyanite, andalusite, orsillimanite), micro silica, bauxite, chromium oxide and combinationsthereof. The portion of the formulation having diameters in the range of0.01 to 10 micrometers, also known as the fines, may contain reactivealuminas and fume silicas.

The matrix may also contain dispersing agents, plasticizers,anti-foaming or foaming agents and de-airing components. These agentsare well known in the art.

The method of the invention produces castable mixtures with a minimalvolume of fine grains. Generally, the amount of fine grains needed tocreate a castable is dependent on the size of the top size grain. Mixeswith a top grain size of 3 mesh typically need a minimum of 33 volumepercent −100 mesh grains to form a functional castable mixture. Usefulcastable mixtures with 30 volume percent or less −100 mesh grains, 29volume percent or less −100 mesh grains, 26 volume percent or less −100mesh grains, 25 volume percent or less −100 mesh grains, 22 volumepercent or less −100 mesh grains or from, and including, 24 volumepercent to, and including, 18 volume percent −100 mesh grains, can beproduced according to the present invention.

Castable mixtures with a 3 mesh top grain size typically require aminimum of 48 volume percent −16 mesh grains to form a functionalcastable mixture. Useful castable mixtures with 47 volume percent orless −16 mesh grains, 45 volume percent or less −16 mesh grains, or 43volume percent or less −16 mesh grains, can be produced according to thepresent invention.

Castable mixtures with a 3 mesh top grain size typically need a minimumof 58 volume percent −6 mesh grains to form a functional castablemixture. Useful castable mixtures with 55 volume percent or less −6 meshgrains, 47 volume percent or less −6 mesh grains, 42 volume percent orless −6 mesh grains, or 36 volume percent or less −6 mesh grains can beproduced according to the present invention. Regardless of the top grainsize, a minimum volume of fine aggregate is needed for prior artcastable mixtures. These minimum volumes are similar to the values givenfor mixes with a top grain size of 3 mesh. Mesh values are expressedhere as Tyler values.

Additionally, the maximum volume percent values for −6 mesh grains, −14mesh grains, −16 mesh grains, −28 mesh and −100 mesh grains presentedfor castable mixtures with a top grain size of 3 mesh may also be usedto produce castable mixtures according to the invention having a topgrain size or aggregate larger than 3 mesh. For example, −⅜″ aggregates,½″×¼″ aggregates, −½″ aggregates, −¾″ aggregates and −1″ aggregates,mixtures of these aggregates and aggregates having a top grain sizewithin the range of, and including, −3 mesh and 12″ may be used toproduce castable compositions according to this invention.

The method of the invention produces cast bodies with densitiespreviously unattainable for the compositions used. Alumina-based castobjects of the prior art may have densities up to 202 pounds per cubicfoot in the green state if they incorporate chromium oxide. Green statematerials contain free water; this water is removed by heating to 230°F. Alumina-based cast objects with densities, in the green state, of 204pounds per cubic foot or greater, or 210 pounds per cubic foot orgreater, can be produced according to the present invention.

Alumina-based cast objects of the prior art may have densities up to 199pounds per cubic foot after drying to 230° F. if they incorporatechromium oxide, or 196 pounds per cubic foot in the green state if theyincorporate only aluminas. Alumina-based cast objects with densities,after drying to 230° F., of 200 pounds per cubic foot or greater, 202pounds per cubic foot or greater, or 207 pounds per cubic foot orgreater, can be produced according to the present invention.

The method of the present invention produces cast bodies with densities,with respect to theoretic densities, previously unattainable. Thetheoretic density refers to the highest density attainable for asubstance (i.e., a solid sample containing no gaps, as distinguishedfrom a packed powder having gaps between particles). Alumina has atheoretic density of 247.53 pounds per cubic foot. The prior art canproduce materials with (196.0/247.53)×100% or 79.2% of theoreticdensity, or (199.0/247.53)×100% or 80.3% of theoretic density. Materialsproduced according to the present invention may have (200.0/247.53)×100%or 80.7% of theoretic density or greater, or densities that equal orexceed 83.6% of theoretic density.

The method of the invention enables the production of castable materialwith a reduced quantity of liquid. Prior art castable materialstypically contain at least 3.7 wt % liquid. Castable material can beproduced according to the present invention with 3.3 wt % liquid orless, 3.0 wt % liquid or less, 2.0 wt % liquid, or 1.7 wt % liquid orless. Prior art castable materials typically contain at least 10.9 vol %liquid. Castable material can be produced according to the presentinvention with 9.1 vol % liquid or less, or 7.8 vol % liquid or less.These percentages are expressed with respect to a total weight or volumeof aggregate, matrix, fines and water.

The method of the invention enables the production of cast bodies withreduced porosity. Cast bodies produced by prior art casting techniqueshave, after heating to 1500° F., porosity levels of no less than 13%.Cast bodies can be produced according to the present invention withporosity levels less than 13%, less than 12%, less than 11%, less than10%, less than 9%, less than 8%, less than 7%, less than 6%, less than5%, less than 4%, or less than 3%.

In a process according to the invention, cast shapes, cast structuresand cast products, such as columnar structures, may be constructed withthe castable compositions of the invention. The method comprises stepsof (a) providing a mold having a cavity which corresponds to the sizeand shape of the structure or cast product, (b) filling the cavity witha castable composition of the invention, (c) optionally subjecting thecastable composition of the invention to compacting and/or vibration,(d) curing the castable composition to form the cast shape, caststructure or cast product, and (e) separating the mold from the castshape, cast structure or cast product. The compositions of the presentinvention may also be used in a compression forming procedure, in whichthe wet composition is placed in a mold and subjected to mechanical orhydraulic pressing or other compression processes to form a piece orcast product of the desired shape.

The castable compositions of the invention may be heated to obtain goodgreen strengths for demolding. Heating to 110° C. may be used to reactthe reactive alumina. Alternatively, or in addition, a cement may beused in the fine-grained material to provide green strength.

The examples presented in Table I were cast using tabular alumina sizedas indicated and Secar 71 cement as a binder. Secar 71 is a hydraulicbinder with an alumina content of approximately 70%. ULM2 is acomposition of the present invention having four peaks in particlediameter distribution; two of the peaks correspond to particles havingdiameters of 250 micrometers or less. ULM3 and ULM3B are twocompositions of the present invention having three particle diameterdistribution peaks corresponding to particles having diameters of 1000micrometers or less. PA1 and PA2 are prior art compositions. ULM1 is acomposition of the present invention that was derived from compositionPA2 by alteration of the particle distribution of the sub-100-micrometer(or −60 mesh) range, and by introduction of gaps in that range.

The “loading” values in Tables I and II represent remaining weightpercentages, defined as the percentage by weight of particles in a givenfraction with respect to the weight of all particles in the fractionplus all smaller particles. For example, the fraction containing thelargest particles in ULM2 contains 53 wt % of the alumina and silica inthe composition. The fraction containing the second-largest particlescontains 50 wt % of the remaining particles. The fraction containing thethird-largest particles contains 35 wt % of the remaining particles. Thefraction containing the fourth-largest particles, which are also thesmallest particles, contains 100 wt % of the remaining particles.

The compositions ULM 1, ULM 3 and ULM3B contain four or more fractionshaving an alternating remaining weight configuration. PA1 and PA2 lacksuch a configuration. ULM2 also lacks a four-fraction alternatingremaining weight configuration, but does have two peaks corresponding toparticles having diameters of 250 micrometers or less.

The compositions PA1 and PA2 required the quantities of water shown(6.34 wt % and 5.25 wt % respectively) to produce a cast product.

A3000FL is a superground, bimodal reactive alumina with a d50 ofapproximately 2.5-3 micrometers and a specific surface area measured bythe BET (Brunauer-Emmett-Teller) method of typically 1.3-2 square metersper gram. A152SG is a superground alumina having a monomodal particlesize distribution with a median particle size of 1.2 micrometers. RG4000 is a monomodal reactive alumina with a d50 of 0.5-0.8 micrometers.Dispex N100 is a sodium polyacrylate dispersant.

Present invention ultra-low matrix compositions ULM1, ULM2, ULM3 andULM3B show increases in MOR, bulk density, and CCS, and decreasedporosity when compared with prior art compositions PA1 and PA2. Thecomponents and properties of these compositions are presented in TableI.

TABLE I Comparison of Components and Physical Properties ULM3 ULM3B PA1PA2 ULM1 ULM2 48/33/ 48/33/ Prior Art Prior Art 40/33/ 53/50/ 48/33/48/33/ 45/45/ 40/33/ 38/33/ Loading 35/100 48/100 48/100 100 38/10048/100 Alumina, Tabular, T-64, 53.00 48.00 −½″ + ¼″ Alumina, Tabular,T-64, 48.00 45.00 40.00 40.00 −3 + 6M Alumina, Tabular, T-1064, 15.026 + 14 Alumina, Tabular, T-1064, 20.80 2.15 15.02 20.00 20.00 14 × 28Alumina, Tabular, T-64, −28M 2.82 Alumina, Tabular, T-64, 11.20 2.1525.00 −28 + 48M Alumina, Tabular, T-64, 10.50 15.00 15.00 −40 + 60MAlumina, Tabular, T-1064, 5.52 6.22 −48M Alumina, Tabular, T-64, 8.185.98 5.98 26.00 21.00 8.28 −100M Cement, Secar 71 (Domestic) 4.00 4.004.00 4.00 4.00 4.00 Alumina, White Fused, 1.64 1.64 3.82 −325M Alumina,Reactive, A3000FL 3.88 1.86 1.86 2.58 Alumina, Reactive, A152SG 4.262.04 2.04 2.83 Alumina, Reactive, RG4000 1.29 0.62 0.62 0.86 Silica Fume971 1.62 1.90 1.90 2.63 Boric Acid Powder 0.02 0.02 0.02 0.02 0.02 0.02Dispex N100 0.05 0.05 0.05 0.05 0.05 0.05 Water 2.30 2.25 2.50 6.34 5.252.10 Properties MOR (psi) 230 F. 4,600 3,900 4,700 700 800 4,100 MOR(psi) 1500 F. 7,000 6,200 6,100 300 400 8,300 Bulk Density (pcf) 230 F.209 207 203 186 187 203 Bulk Density (pcf) 1500 F. 207 205 201 183 183201 Porosity (%) 230 F. 1.4 1.9 2.6 17.7 17.0 1.3 Porosity (%) 1500 F.6.9 7.8 7.7 20.2 20.2 4.1 CCS (psi) 230 F. 16,900 12,600 15,200 1,5002,200 13,100 CCS (psi) 1500 F. 15,700 17,300 11,700 1,800 1,800 14,600

Present invention compositions ULM-FG, ULM-PG and ULM-671 are able toproduce cast shapes with decreased percentages of water when comparedwith prior art composition PA2. Compositions are presented in Table II;a comparison of properties of cast shapes produced with the addition ofvarious proportions of water is presented in Table III.

TABLE II Comparison of Compositions ULM-FG ULM-PG ULM-671 PA2 40/30/40/30/ 40/30/ 40/33/ 40/30/ 40/30/ 40/30/ Loading 38/100 40/100 40/10040/100 Alumina, Tabular, T-64, −½″ + ¼″ — — — — Alumina, Brown Fused,−⅜ + 3M 40.00 40.00 Alumina, Tabular, T-64, −3 + 6M 40.00 40.00 Alumina,Tabular, T-1064, 6 + 14 18.00 15.75 Alumina, Tabular, T-1064, 14 × 2820.00 2.25 18.00 Alumina, Tabular, T-64, −28M Alumina, Tabular, T-64,−28 + 48M 16.80 11.26 Alumina, Tabular, T-64, −40 + 60M 15.00 16.80Alumina, Tabular, T-1064, −48M 5.54 Alumina, Tabular, T-64, −100M 21.007.56 7.56 7.56 Cement, Secar 71 (Domestic) 4.00 4.00 4.00 4.00 Alumina,White Fused, −325M 2.84 2.84 2.84 Alumina, Reactive, A3000FL 3.13 3.133.13 Alumina, Reactive, A152SG 3.44 3.44 3.44 Alumina, Reactive, RG40001.04 1.04 1.04 Silica Fume 971 3.20 3.20 3.20 Boric Acid Powder 0.020.02 0.02 0.02 Dispex N100 0.05 0.05 0.05 0.05 Water 2.00-6.00 2.00-6.002.00-3.00 2.00-3.00

All samples were subjected to 30 seconds of dry mixing, 4.5 minutes ofwet mixing, 4 minutes of high vibration and 1 minute of low vibration.KBD values are bulk densities measured in pounds per cubic foot. KPORvalues are porosity values measured as volume percent. Both the KBDvalues and KPOR values are 1500 degree F. values. The designation DNB isgiven to compositions that did not bond. The designation DNC is given tocompositions that did not consolidate.

In certain compositions, such as the ultra-low-matrix compositions ofthe present invention in which high proportions of water were added forcomparison purposes, segregation of particle fractions was observed.Table values designated as “full” are measurements of piecesrepresenting a complete top-to-bottom cross section of a sample. Tablevalues designated as “bottom” are measurements of a portion of a samplecloser to the vibration source. Percentages of water in Table III areweight percentages.

TABLE III Properties of Pieces Cast from Prior Art and Present InventionCompositions KBD KPOR KBD Avg. KPOR Avg. Avg. Avg. Observations FullFull Bottom Bottom PA2 DNB — — — — 2 wt % water DNC PA2 DNC 163.1 28.1163.2 27.1 3 wt % water PA2 DNC 164.2 25.7 163.1 26.6 4 wt % water PA2190.6 17.2 193.9 16.2 5 wt % water PA2 Wet 188.1 18.7 190.0 17.7 6 wt %water ULM - FG 210.4 4.9 206.3 3.9 2 wt % water ULM - FG 211.2 7.8 210.16.6 3 wt % water ULM - FG Wet 206.5 9.8 211.1 7.4 4 wt % water ULM - FGWet 202.9 11.6 210.8 8.6 5 wt % water ULM - FG Wet 198.6 14.0 209.5 9.56 wt % water ULM - PG 209.8 4.5 205.7 5.0 2 wt % water ULM - PG 211.17.9 212.4 6.0 3 wt % water ULM - 671 DNB — — — — 2 wt % water DNC ULM -671 201.6 6.7 197.7 8.8 3 wt % water

FIG. 1 contains a comparison of a particle size distribution 12according to the prior art with a particle size distribution 14according to the present invention. Particle size distribution 14corresponds to composition ULM 2 in Table I. In this figure, the weightpercentages for particles in the dry composition are plotted as afunction of particle sizes (expressed in micrometers on a logarithmicscale).

Criterion SR 92 CF is a fine particle material that may be used toproduce cast bodies according to the prior art. It contains a fineactivated alumina binder. Its grain size distribution, expressed inmesh, and its chemical composition are compared, in Tables IV and V,with that of a fine particle material, exhibiting a particle size gap,according to the present invention.

TABLE IV Comparison of Particle Size Fractions of the Invention with thePrior Art Criterion SR 92 CF, Material of the invention, percent percent +3M 0.0 41.7 3 × 4M 0.3 5.5 4 × 6M 15.8 9.9 6 × 8M 7.3 0.6  8 × 12M 5.60.0 12 × 16M 4.7 0.2 16 × 20M 8.4 3.2 20 × 30M 6.3 2.7 30 × 40M 3.5 1.540 × 50M 7.6 4.5 50 × 70M 3.2 1.9  70 × 100M 2.6 1.6 −100M 34.6 26.7

TABLE V Comparison of the Chemical Composition of the Invention with thePrior Art Criterion SR 92 CF, Material of the invention, weight percentweight percent SiO₂ 1.1 1.8 Fe₂O₃ 0.1 0.1 Al₂O₃ 87.1 91.7 MgO 5.6 3.5CaO 0.0 0.1 Na₂O 0.2 0.2 P₂O₅ 0.0 0.0 K₂O 0.0 0.0 Cr₂O₃ 0.0 0.0 TiO₂ 0.00.0 B₂O₃ 0.0 0.0 ZrO₂ 0.0 0.0 SiC 0.0 0.0 C 0.0 0.0 Other 0.0 0.0 LOI5.9 2.7

FIG. 2 depicts a particle size distribution according to the presentinvention in which six fractions have an alternating remaining weightpercentage configuration, alternating between 33% and 48% until thefinal fraction is reached. Although the weight percentages of thefractions decrease with decreasing particle size until the last fractionis reached, the six largest fractions exhibit an alternating remainingweight percentage configuration. The first fraction 21 contains 33 wt %of the particles; 67 wt % of the particles remain. The second fraction22 contains (67*0.48) or 32.2 wt % of the particles. The first twofractions thus contain 65.2 wt %; 34.8 wt % remain. The third fraction23 contains (34.8*0.33) or 11.5 wt % of the particles. The first threefractions thus contain 76.7 wt %; 23.3 wt % remain. The fourth fraction24 contains (23.3*0.48) or 11.2 wt % of the particles. The first fourfractions thus contains 87.9 wt %; 12.1 wt % remain. The fifth fraction25 contains (12.1*0.33) or 4.0 wt % of the particles. The first fivefractions thus contain 91.9 wt %; 8.1 wt % remain. The sixth fraction 26contains (8.1*0.48) or 3.9 wt %. The first six fractions thus contain95.8 wt %; 4.2 wt % remain. The seventh fraction 27 is the only fractionremaining, so it contains 4.2 wt % of the particles, or 100 wt % of theparticles remaining

FIG. 3 depicts the particle size distribution for ULM3, a composition ofthe present invention. In this figure, the volume percentages forparticles in the dry composition are plotted as a function of particlesizes, expressed in micrometers, on a logarithmic scale. First fraction31, second fraction 32, third fraction 33, fourth fraction 34, fifthfraction 35 and sixth fraction 36 are shown. First fraction 31 has aremaining volume percentage of 48%. The remaining volume percentage is32% for second fraction 32, 42% for third fraction 33, 48% for fourthfraction 34, and 44% for fifth fraction 35. The remaining volumepercentage is the percentage of the volume of particles in the indicatedrange with respect to the sum of the volume of particles in all rangesin which particles have the same or smaller diameters than in theindicated range. Sixth fraction 36, the fraction containing the smallestparticles, has a remaining volume percentage of 100%.

FIG. 4 depicts the particle size distribution for ULM3B, a compositionof the present invention. In this figure, the volume percentages forparticles in the dry composition are plotted as a function of particlesizes, expressed in micrometers, on a logarithmic scale. First fraction41, second fraction 42, third fraction 43, fourth fraction 44, fifthfraction 45 and sixth fraction 46 are shown. First fraction 41 has aremaining volume percentage of 48%. The remaining volume percentage is30% for second fraction 42, 41% for third fraction 43, 41% for fourthfraction 44, and 49% for fifth fraction 45. The remaining volumepercentage is the percentage of the volume of particles in the indicatedrange with respect to the sum of the volume of particles in all rangesin which particles have the same or smaller diameters than in theindicated range. Sixth fraction 46, the fraction containing the smallestparticles, has a remaining volume percentage of 100%.

FIG. 5 contains a plot of percentage by mass of particle fractions withrespect to particle diameter in micrometers of PA1, a composition of theprior art. The plot depicts first fraction 51, second fraction 52 andthird fraction 53. Third fraction 53 contains all the material in thecomposition having a diameter of 100 micrometers or less, and exhibits asingle peak. First fraction 51 contains 45 percent of the remainingweight, second fraction 52 contains 46 percent of the remaining weight,and third fraction 53 contains 100 percent of the remaining weight.

FIG. 6 contains a plot of percentage by mass of particle fractions withrespect to particle diameter in micrometers of PA2, a composition of theprior art. The plot depicts first fraction 61, second fraction 62, thirdfraction 63 and fourth fraction 64. Fourth fraction 64 contains all thematerial in the composition having a diameter of 100 micrometers orless, and exhibits a single peak. First fraction 61 contains 40 percentof the remaining weight, second fraction 62 contains 33 percent of theremaining weight, third fraction 63 contains 38 percent of the remainingweight, and fourth fraction 64 contains 100 percent of the remainingweight.

FIG. 7 contains a plot of percentage by mass of particle fractions withrespect to particle diameter in micrometers of ULM1, a composition ofthe present invention. The plot depicts first fraction 72, secondfraction 72, third fraction 73, fourth fraction 74, fifth fraction 75,and sixth fraction 76. Fractions 71, 72 and 73 contain the same weightpercent as the analogous fractions in PA2. However, thesub-1000-micrometer portion of the PA2 particle distribution exhibits asingle peak, whereas the sub-1000-micrometer portion of ULM1 exhibitsthree fractions, namely fractions 74, 75 and 76.

The invention encompasses:

1. A castable composition producing, when cast with a water content of2.8 wt % or less, a cast product having a porosity equal to or less than15 volume percent when measured after exposure to 230 degrees F.

2. A castable composition producing, when cast with a water content of2.8 wt % or less, a cast product having a modulus of rupture equal to orgreater than 1000 pounds per square inch as measured after exposure to230 degrees F.

3. A castable composition producing, when cast with a water content of2.8 wt % or less, a cast product having a cold crushing strength equalto or greater than 3000 pounds per square inch as measured afterexposure to 230 degrees F.

4. A castable composition according to claim 1, wherein the cast producthas a porosity equal to or less than 10 volume percent as measured afterexposure to 230 degrees F.

5. A castable composition according to claim 1, wherein the cast producthas a porosity equal to or less than 9 volume percent as measured afterexposure to 230 degrees F.

6. A castable composition according to claim 1, wherein the cast producthas a porosity equal to or less than 8 volume percent as measured afterexposure to 230 degrees F.

7. A castable composition according to claim 1, wherein the cast producthas a porosity equal to or less than 7 volume percent as measured afterexposure to 230 degrees F.

8. A castable composition according to claim 1, wherein the cast producthas a porosity equal to or less than 6 volume percent as measured afterexposure to 230 degrees F.

9. A castable composition according to claim 1, wherein the cast producthas a porosity equal to or less than 5 volume percent as measured afterexposure to 230 degrees F.

10. A castable composition according to claim 1, wherein the castproduct has a porosity equal to or less than 4 volume percent asmeasured after exposure to 230 degrees F.

11. A castable composition according to claim 1, wherein the castproduct has a porosity equal to or less than 3 volume percent asmeasured after exposure to 230 degrees F.

12. A castable composition according to any of claims 1, 4, 5, 6, 7, 8,9, 10 and 11, wherein the porosities are obtained by measurement afterexposure to 1500 degrees F.

13. A castable composition according to claim 2, wherein the castproduct has a modulus of rupture equal to or greater than 2000 poundsper square inch as measured after exposure to 230 degrees F.

14. A castable composition according to claim 2, wherein the castproduct has a modulus of rupture equal to or greater than 3000 poundsper square inch as measured after exposure to 230 degrees F.

15. A castable composition according to claim 2, wherein the castproduct has a modulus of rupture equal to or greater than 4000 poundsper square inch as measured after exposure to 230 degrees F.

16. A castable composition according to any of claims 2, 13, 14 and 15,wherein the modulus of rupture values are obtained by measurement afterexposure to 1500 degrees F.

17. A castable composition according to claim 3, wherein the castproduct has a cold crushing strength of 5000 pounds per square inch asmeasured after exposure to 230 degrees F.

18. A castable composition according to claim 3, wherein the castproduct has a cold crushing strength of 8000 pounds per square inch asmeasured after exposure to 230 degrees F.

19. A castable composition according to claim 3, wherein the castproduct has a cold crushing strength of 10,000 pounds per square inch asmeasured after exposure to 230 degrees F.

20. A castable composition according to claim 3, wherein the castproduct has a cold crushing strength of 12,000 pounds per square inch asmeasured after exposure to 230 degrees F.

21. A castable composition according to any of claims 3, 17, 18, 19 and20, wherein the cold crushing strength is obtained by measurement afterexposure to 1500 degrees F.

22. A castable composition according to any of claims 1-21,characterized by a coarsest refractory grain fraction comprising atleast 50% by weight of the dry composition, and wherein the coarsestrefractory grain fraction is separated from a smaller grain fraction bya gap having a ratio of largest particle diameter to smallest particlediameter of at least the square root of 2.

23. A castable composition according to any of claims 1-21, in which thecomposition contains at least four grain fractions, of which threeadjacent grain fractions are separated by gaps having a particlediameter ratio of at least the square root of two, and the threeadjacent grain fractions have remaining weight percentages that are,with respect to the respective immediately larger particle sizefractions and in order of decreasing particle size, smaller, larger andsmaller in value.

24. A castable composition according to any of claims 1-21, in which thecomposition contains at least four grain fractions, of which threeadjacent grain fractions are separated by gaps having a particlediameter ratio of at least the square root of two, and the threeadjacent grain fractions have remaining weight percentages that are,with respect to the respective immediately larger particle sizefractions and in order of decreasing particle size, larger, smaller, andlarger in value.

25. A castable composition according to any of claims 1-21, wherein thecomposition contains at least two grain fractions separated by gapshaving a particle diameter ratio of at least the square root of two, andthe at least two grain fractions are entirely composed of particles withdiameters less than 100 micrometers.

26. A castable composition according to any of claims 1-21, wherein thecomposition contains at least three grain fractions separated by gapshaving a particle diameter ratio of at least the square root of two, andthe at least three grain fractions are entirely composed of particleswith diameters less than 100 micrometers.

27. A castable composition according to any of claims 1-21, wherein thecomposition contains at least four grain fractions separated by gapshaving a particle ratio diameter of at least the square root of two, andthe remaining weight percentages are at least 40% in each of the atleast four grain fractions.

28. A castable composition according to any of claims 1-21, wherein thecomposition contains at least five grain fractions separated by gapshaving a particle ratio diameter of at least the square root of two.

29. A castable composition according to any of claims 23-28, wherein atleast two of the gaps each contain less than 10 percent by mass of themass of the dry composition.

30. A castable composition according to any of claims 23-28, wherein atleast two of the gaps each contain less than 5 percent by mass of themass of the dry composition.

31. A castable composition according to any of the preceding claims,wherein the cast product has a density that is at least 80.7% of thetheoretic density.

32. A castable composition according to any of the preceding claims,wherein the cast product has a density that is at least 83.6% of thetheoretic density.

33. A castable composition according to any of the preceding claims,comprising at least 95 wt % alumina.

34. A castable composition according to claim 33, wherein the castproduct has a bulk density of at least 190 pounds per cubic foot asmeasured at 230 degrees F.

35. A castable composition according to claim 33, wherein the castproduct has a bulk density of at least 195 pounds per cubic foot asmeasured at 230 degrees F.

36. A castable composition according to claim 33, wherein the castproduct has a bulk density of at least 200 pounds per cubic foot asmeasured at 230 degrees F.

37. A castable composition according to claim 33, wherein the castproduct has a bulk density of at least 202 pounds per cubic foot asmeasured at 230 degrees F.

38. A castable composition according to claim 33, wherein the castproduct has a bulk density of at least 207 pounds per cubic foot asmeasured at 230 degrees F.

39. A castable composition according to any of claims 34-36, wherein thebulk density is measured at 1500 degrees F.

40. A cast product produced from a castable composition according to anyof claims 1-39.

41. A method for producing a cast product, comprising, (a) providing amold having a cavity which corresponds to the size and shape of theproduct, (b) filling the cavity with a castable composition according toany of claims 1-39, (c) optionally subjecting the castable compositionof the invention to compacting and/or vibration, (d) curing the castablecomposition to form the cast product, and (e) separating the mold fromthe cast product.

42. A method for producing a cast product, comprising, (a) providing amold having a cavity which corresponds to the size and shape of theproduct, (b) filling the cavity with a castable composition according toany of claims 1-39, (c) subjecting the castable composition of theinvention to a compression process, (d) curing the castable compositionto form the cast product, and (e) separating the mold from the castproduct.

What is believed to be the best mode of the invention has been describedabove. However, it will be apparent to those skilled in the art thatnumerous variations of the type described could be made to the presentinvention without departing from the spirit of the invention. The scopeof the present invention is defined by the broad general meaning of theterms in which the claims are expressed.

I claim:
 1. A castable composition comprising refractory material,wherein the composition comprises: a) a first grain fraction consistingof particles with diameters less than 100 micrometers; b) a second grainfraction consisting of particles with diameters less than 100micrometers; and c) a plurality of adjacent grain fractions separated bygaps having a particle diameter ratio of the square root of two, theplurality of grain fractions consisting of particles with diametersgreater than 100 micrometers.
 2. A castable composition according toclaim 1, further comprising a third grain fraction consisting ofparticles with diameters less than 100 micrometers.
 3. A castablecomposition according to claim 2, further comprising a fourth grainfraction consisting of particles with diameters less than 100micrometers.
 4. A castable composition according to claim 3, furthercomprising a fifth grain fraction consisting of particles with diametersless than 100 micrometers.
 5. A castable composition according to claim3, wherein the first grain fraction, the second grain fraction, thethird grain fraction and the fourth grain fraction comprise a materialselected from the group consisting of alumina and Secar cement.
 6. Acastable composition according to claim 1, wherein the compositionconsists of more than 4 dry weight percent of particles with diametersless than 100 micrometers.
 7. A castable composition according to claim1, wherein the composition consists of more than 13 dry weight percentof particles with diameters less than 100 micrometers.
 8. A castablecomposition according to claim 1, further comprising silica fume.
 9. Acastable composition according to claim 1, wherein the coarsestrefractory grain composition comprises at least 50% by weight of the drycomposition.
 10. A castable composition according to claim 1, whereinthe gap contains less than 10% by mass of the dry composition.
 11. Acastable composition according to claim 1, wherein the gap contains lessthan 5% by mass of the dry composition.
 12. A castable compositionaccording to claim 1, comprising at least 95 dry weight percent alumina.13. A castable composition according to claim 1, wherein the coarsestrefractory grain comprises at least 50% by weight of the composition.14. A method for producing a cast product, comprising, (a) providing amold having a cavity which corresponds to the size and shape of theproduct, (b) filling the cavity with a castable composition according toclaim 1, (c) optionally subjecting the castable composition of theinvention to compacting and/or vibration, (d) curing the castablecomposition to form the cast product, and (e) separating the mold fromthe cast product.
 15. A method for producing a cast product, comprising,(a) providing a mold having a cavity which corresponds to the size andshape of the product, (b) filling the cavity with a castable compositionaccording to claim 1, (c) subjecting the castable composition of theinvention to a compression process, (d) curing the castable compositionto form the cast product, and (e) separating the mold from the castproduct.